Communication Using a Spacer Fluid

ABSTRACT

Disclosed are systems and methods for transmitting commands from a surface to downhole electronic equipment using pills of a spacer fluid. One method of communicating down a wellbore may include providing a flow of a first fluid along a flow path, introducing a series of one or more pills of a second fluid into the flow of the first fluid at a first point along the flow path, and detecting the series of one or more pills of the second fluid at a second point along the flow path, the second point being separated from the first point. In certain embodiments, a series of brine pills may be introduced into a flow of a drilling fluid.

BACKGROUND

The present invention relates generally to downhole communicationsystems and methods and, more particularly, to systems and methods fortransmitting commands from the surface to downhole electronic equipmentusing pills of a spacer fluid.

Modern hydrocarbon drilling and production operations requires the useof electronic equipment in the downhole environment. For example, adrill string or accompanying bottom-hole assembly may include activesensors that obtain information about the downhole environment such asthe various characteristics and parameters of the earth formationstraversed by the borehole, data relating to the size and configurationof the borehole itself, pressures and temperatures of ambient downholefluids, and other vital downhole parameters. Furthermore, it may beadvantageous to remotely activate a downhole tool, such as a reamer,only after the tool is in position and to be able to select one of aplurality of functions after the tool is activated.

Providing command signals to the downhole electronic equipment can beproblematic for a number of reasons. Electrical signal wires runningdown the bore hole may become cut by abrasion or twisted and broken bythe turning drill string. Also, the ambient downhole environment mayinterfere with reception of acoustic signals sent from the surface and,in addition, signal attenuation for a deep well may reduce the strengthof an acoustic signal below a reception threshold of the equipment evenin the absence of interference.

In certain drilling locations, the equipment required to provide commandsignals via conventional methods, such as acoustic pulses, may not beavailable while it is still desirable to send a signal to a piece ofdownhole electronic equipment. Moreover, in certain drilling locations,the ambient conditions may have an adverse effect on sensitive surfaceequipment and it may be advantageous to use more robust methods to sendcommands to downhole equipment.

SUMMARY OF THE INVENTION

The present invention relates generally to downhole communicationsystems and methods and, more particularly, to systems and methods fortransmitting commands from the surface to downhole electronic equipmentusing pills of a spacer fluid.

In certain embodiments, a method of communicating is disclosed that mayinclude the steps of providing a flow of a first fluid along a flowpath, introducing a series of one or more pills of a second fluid intothe flow of the first fluid at a first point along the flow path, anddetecting the series of one or more pills of the second fluid at asecond point along the flow path that is separated from the first point.

In certain embodiments, a communication system is disclosed that mayinclude a fluid valve having a first input fluidly coupled to a sourceof a first fluid exhibiting a first value of a physical property, asecond input fluidly coupled to a source of a second fluid exhibiting asecond value of the physical property, and an output fluidly couplingthe first and second inputs to a flow path. The communication system mayalso include a controller communicatively coupled to the fluid valve andconfigured to actuate the fluid valve so as to provide a flow of thefirst fluid to the flow path and introduce a series of one or more pillsof the second fluid into the flow of the first fluid. The communicationsystem may also include a sensor arranged within the flow path andconfigured to detect the physical property and differentiate between thefirst value and the second value, thereby detecting the series of one ormore pills of the second fluid.

In certain embodiments, a method of communicating with a downhole toolis disclosed that may include the step of providing a flow of a drillingfluid from a surface valve through a drill string to the downhole tool,wherein the drilling fluid exhibits a first value of a physicalproperty. The method may also include the step of introducing one ormore pills of a spacer fluid into the flow of the drilling fluid via thesurface valve, wherein the spacer fluid exhibits a second value of thephysical property that is different from the first value. The method mayalso include the step of detecting the one of more pills of the spacerfluid at the downhole tool.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent invention, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, as willoccur to those skilled in the art and having the benefit of thisdisclosure.

FIG. 1 illustrates a land-based oil and gas rig including a downholecommunication system that may be employed to provide signals to one ormore downhole electronics, equipment, or tools, according to one or moreembodiments.

FIG. 2 is a schematic diagram of an exemplary communication systemconfigured to provide a signal down a drill string, according to one ormore embodiments.

FIG. 3 is a block diagram of an exemplary communicative coupling of thevalve controller and the downhole electronics, according to one or moreembodiments.

FIGS. 4A-4E depict example messages comprising pills of a second fluidinjected into a flow of a first fluid, according to one or moreembodiments.

FIGS. 5A-5C depict movement of an example message from the valve to thedownhole sensor, according to one or more embodiments.

FIGS. 6A and 6B illustrate the ideal configuration of a series of pillsof a second fluid injected into a flow of a first fluid through a pipe,according to one or more embodiments.

FIGS. 7A and 7B illustrate a downstream configuration of the same seriesof pills of a second fluid injected into a flow of a first fluid througha pipe, according to one or more embodiments.

DETAILED DESCRIPTION

The present invention relates generally to downhole communicationsystems and methods and, more particularly, to systems and methods fortransmitting commands from the surface to downhole electronic equipmentusing pills of a spacer fluid.

The disclosed embodiments facilitate digital communication with one ormore downhole tools and/or mechanisms when conventional communicationsystems, such as electrical wires or fiber-optic cable, prove untenable.Such digital communication may be used to trigger activation or changesin operating methods or parameters of the one or more downhole toolsand/or mechanisms. One or more of the disclosed embodiments allowsignals to be sent along a flow path through which a first fluid isflowing using one or more pills of a second fluid injected into the flowof the first fluid. This allows information and commands to be sentdownstream along the flow path in the absence of a separatecommunication system running parallel to the flow path.

One or more of the disclosed embodiments allow command signals to besent from a drill rig on the surface to a downhole electronics systemvia one or more pills of a spacer fluid injected into the existing flowof drilling fluid, i.e., mud, that is already flowing down the entirelength of the drill string. This method is particularly advantageous atdrill sites where conventional communication equipment, such as anacoustic pulser, are not available or where the ambient conditions havea detrimental effect on the operation of such equipment.

As used herein, the term “pill” or variations thereof refers to acoherent quantity of a second fluid that is introduced into a flow of afirst fluid through a flow path, such as a pipe, a tube, or an annulusdefined between a pipe and a wellbore, for example. The term “pill” maybe considered equivalent to the term “spacer” and/or the phrase “fluidspacer.” One example of a pill is an air bubble that is injected into aflow of water through a tube. In this example, the water would beconsidered the first fluid and the air would be considered the secondfluid; the air bubble forming a pill of the second fluid within the flowof the first fluid. In some embodiments, a pill may fill the entirecross-section of the flow path through which it is conveyed or otherwiseflowing.

A pill may be characterized as a homogenous geographical region ofmaterial that defines one or more borders, divisions, or end surfacesbetween adjacent fluids or substances. While the borders, divisions, orend surfaces of the pill may not necessarily exhibit planar surfacesoriented perpendicular to the flow of the first fluid, a pill maynonetheless be considered to have a definable length between a leadingend surface and a trailing end surface. As will be appreciated, thelength of the pill may change as the pill travels along the flow pathdue to intermixing and/or distortion of the first and second fluids atthe opposing surface and trailing end surfaces due to, for example,viscous friction caused by the surrounding rigid structure of the flowpath. Pills may be formulated to have specific density and/orrheological properties to help maintain pill integrity and minimizedmixing as the pill travels along the flow path. This is a well-knowntechnique for spacer/pill design.

As used herein, the phrase “spacer fluid” or variations thereof refer toany second fluid that is injected into a flow of a first fluid, therebyproviding a definable gap in the first fluid. The spacer fluid may alsobe used to physically separate one special-purpose fluid from another ina flow of fluid, or otherwise provide a function that is not provided bythe first fluid. An example special-purpose fluid related to the oil andgas industry is a drilling fluid or mud that may be conveyed into awellbore to power and cool a drill bit and subsequently carry materialremoved by the drill bit back to the surface. Certain special-purposefluids may be prone to contamination, so that a pill of a spacer fluidmay be introduced into a flow of a first fluid immediately prior to thespecial-purpose fluid so as to separate the special-purpose fluid fromthe first fluid. Exemplary spacer fluids include, but are not limited towater, brines, viscosified brines, viscosified water, weighted andviscosified oil-based or water-based drilling fluids, weighted andviscosified brines, oils, combinations thereof, and the like. In someembodiments, chemicals may be added to enhance the performance of thespacer fluid for a particular operation. In at least one embodiment, apill may be formed of a spacer fluid having certain physical propertiessuch as, but not limited to, surface tension, density, opacity,capacitance, conductivity, magnetism, a particular solids content,salinity, a particular oil/water ratio, a particular refractive index, achemical concentration, a spectral fingerprint, combinations thereof, orthe like.

As used herein, the phrase “magnetic field strength” or variationsthereof refer to any measure of the strength of a magnetic field,including either of the “H” field and the “B” field, as measured by anytechnique, such as the Hall effect. This phrase includes “B” fieldcharacteristics “magnetic flux density” as measured in teslas and“magnetic flux” as measured in webers as well as measurements of the “H”field in amperes per meter and, in the broadest sense, includes anymagnetic physical attribute that can be measured such that two sampleshaving different values of a magnetic physical attribute can bedifferentiated.

As used herein, the term “pulse” or variations thereof refer to aportion of a signal that is in a first state when the signal may haveonly either a first state or a second state, i.e., a “digital” signal.The two states may be defined as “high” and “low” or “1” and “0” orother arbitrary designations of two states. As commonly viewed on anoscilloscope, a pulse will have a transition from the low state to thehigh state that is the start of the pulse, a duration or length whereinthe value of the signal is generally high, and a transition from thehigh state to the low state that is the end of the pulse. Within thisdisclosure, a pill of a second fluid injected into a flow of a firstfluid may be considered to be a pulse of the second fluid, as the firstfluid may be considered to be a first state of the flow as the flowpasses a fixed point and the second fluid may be considered to be asecond state of the flow.

As used herein, the term “coherence” or variations thereof refer to thephysical integrity of a pill made up of a second liquid within a flow ofa first fluid as the pill travels through a flow path. Even if a pillstarts in a flow path with an ideal configuration, e.g., a cylinder ofthe second fluid having planar end surfaces, the end surfaces willdeform and diffuse as the pill travels along the tube. Coherence is aqualitative measure of how well the fluid of the pill stays together,wherein a pill is generally considered to still be coherent if theunmixed portion of the second fluid is a large fraction of the originallength of the pill. Another way of viewing coherence is whether theposition of a pill can be determined with an accuracy that is a smallfraction of the distance traveled, for example if the position of a pillcan be determined to an accuracy of a few hundred feet after havingtraveled down a 20,000 foot well.

As used herein, the phrase “electromagnetic radiation” refers to radiowaves, microwave radiation, infrared and near-infrared radiation,visible light, ultraviolet light, X-ray radiation and gamma rayradiation.

As used herein, the term “optical computing device” refers to an opticaldevice that is configured to receive an input of electromagneticradiation from a substance or sample of the substance, and produce anoutput of electromagnetic radiation from a processing element arrangedwithin the optical computing device. The processing element may be, forexample, an integrated computational element (ICE), also known as amultivariate optical element, used in the optical computing device. Theelectromagnetic radiation that optically interacts with the processingelement is changed so as to be readable by a detector, such that anoutput of the detector can be correlated to at least one characteristicof the substance being measured or monitored. The output ofelectromagnetic radiation from the processing element can be reflectedelectromagnetic radiation, transmitted electromagnetic radiation, and/ordispersed electromagnetic radiation.

Whether reflected or transmitted electromagnetic radiation is analyzedby the detector may be dictated by the structural parameters of theoptical computing device as well as other considerations known to thoseskilled in the art. In addition, emission and/or scattering of thesubstance, for example via fluorescence, luminescence, Raman scattering,and/or Raleigh scattering, can also be monitored by the opticalcomputing devices. In some embodiments, suitable structural componentsfor the exemplary optical computing devices are described in commonlyowned U.S. Pat. Nos. 6,198,531; 6,529,276; 7,123,844; 7,834,999;7,911,605; 7,920,258; 8,049,881; and 8,208,147 each of which isincorporated herein by reference in its entirety, and U.S. patentapplication Ser. Nos. 12/094,465 and 13/456,467, each of which is alsoincorporated herein by reference in its entirety. As will beappreciated, variations of the structural components of the opticalcomputing devices described in the above-referenced patents and patentapplications may be suitable, without departing from the scope of thedisclosure, and therefore, should not be considered limiting to thevarious embodiments disclosed herein.

As used herein, the phrase “optically interact” or variations thereofrefers to the reflection, transmission, scattering, diffraction, orabsorption of electromagnetic radiation either on, through, or from oneor more processing elements (i.e., integrated computational elements).Accordingly, optically interacted light refers to electromagneticradiation that has been reflected, transmitted, scattered, diffracted,or absorbed by, emitted, or re-radiated, for example, using theintegrated computational elements, but may also apply to interactionwith a fluid or a substance in the fluid.

As used herein, the term “tool” or variations thereof refer to anydownhole mechanism, sensor, or equipment. A tool may perform, but is notlimited to, an active operation on a portion of a borehole, provide aservice to other downhole equipment, such as a power generator, ormeasure and report on physical properties and attributes of the boreholeor surrounding subterranean formation.

FIG. 1 illustrates a land-based oil and gas rig 100 including a downholetool 140, according to one or more embodiments. It should be noted that,even though FIG. 1 depicts a land-based oil and gas rig 100, it will beappreciated by those skilled in the art that the components of the rig100, and various embodiments of the components disclosed herein, areequally well suited for use in other types of rigs, such as offshoreplatforms, or rigs used in any other geographical location.

As illustrated in FIG. 1, a drilling platform 102 supports a derrick 104having a traveling block 106 for raising and lowering a drill string108. A kelly 110 supports the drill string 108 as it is lowered througha rotary table 112. The kelly 110 may be, for example, a four orsix-sided pipe configured to transfer rotary motion to a turntable 130and the drill string 108. A drill bit 114 is driven either by a downholemotor and/or via rotation of the drill string 108 from the drillingplatform 102 and may include one or more drill collars 127 and 128arranged at or near the drill bit 114. As the bit 114 rotates, itcreates a borehole 116 that passes through various subterraneanformations 118. A pump 120 circulates a drilling fluid (i.e., mud) 126through a feed pipe 122 to the kelly 110, which conveys the drillingfluid 126 downhole through an interior conduit in the drill string 108and through one or more orifices in the drill bit 114. The drillingfluid 126 is then circulated back to the surface via the annulus definedbetween the drill string 108 and the borehole 116 where it is eventuallydeposited in a retention pit 124. The drilling fluid 126 transportscuttings and debris derived from the borehole 116 into the retention pit124 and aids in maintaining the integrity of the borehole 116.

The downhole tool 140 may be coupled to or otherwise form an integralpart of the drill string 108. The downhole tool 140 may berepresentative of any downhole tool or mechanism known to those skilledin the art and may include, but is not limited to, a bit, a reamer, areservoir sampling tool, a downhole power generator, a tool to aid incement placement/position, a wellbore perforation tool, a fluid bypasstool, a Measurement-While-Drilling (MWD) sensor, aLogging-While-Drilling (LWD) sensor, a Magnetic Resonance Imaging (MRI)tool, a Nuclear Magnetic Resonance (NMR) tool, an electromagnetic (EM)telemetry tool, positive or negative mud pulsers, aPressure-While-Drilling (PWD) sensor, a resistivity sensor, combinationsthereof, and the like. These tools and services enable various downholeoperations to be performed, including the capture and/or recording ofvarious critical measurements along with transmitting such data to thesurface, while drilling the borehole 116. These operations andmeasurements make it possible to evaluate the subterranean formation118, maximize drilling performance, and help ensure precise wellboreplacement, thereby helping to reduce time and costs. A tool 140 may haveone or more functions that can be activated or initiated while the tool140 is disposed downhole. For example, a reamer may be lowered to aparticular depth in a retracted configuration, thereby making the reamereasier to handle as the reamer is being lowered into position, and thenthe reamer can be activated by a command as disclosed herein to extendthe reaming blades and commence reaming. Other tool 140, for example aMRI tool, may be lowered in an inactive condition and then activated bya command as disclosed herein to begin making measurements andtransmitting information to the surface.

Referring now to FIG. 2, with continued reference to FIG. 1, illustratedis a schematic diagram of an exemplary communication system 200configured to convey a signal to the downhole tool 140, according to oneor more embodiments. The communication system 200 may include a valve230 that controls the flow of fluids from at least two sources.Specifically, the valve 230 may be configured to control the flow of afirst fluid 126 being drawn from the retention pit 124 using one or morepumps 120. In some embodiments, the first fluid is drilling fluid (i.e.,mud) and may be provided to the valve 230 at a first inlet 231 definedon the valve. The valve 230 may also be configured to control the flowof a second fluid 250 being drawn from a containment vessel or tank 205using one or more pumps 220. The second fluid 250 may be provided to thevalve 230 at a second inlet 232. In one or more embodiments, the valve230 may be configured to fluidly couple either the first inlet 231 orthe second inlet 232 to an outlet 233 defined on the valve 230 andproviding fluid communication to the drill string 108. Accordingly, thevalve 230 may be configured to selectively connect either a flow of thefirst fluid 126 or a flow of the second fluid 250 to the drill string108.

The communication system 200 may also include a controller 235 that, inone or more embodiments, includes a programmable processor and memoryhaving a computer-readable medium (not shown). The controller 235 may becommunicatively coupled to the valve 230 and configured to operate thevalve 230 so as to fluidly connect either the first inlet 231 or thesecond inlet 232 to the outlet 233, thereby providing either a flow ofthe first fluid 126 or a flow of the second fluid 250, respectively, tothe drill string 108. By properly switching back and forth between aflow of the first fluid 126 or a flow of the second fluid 250, asdiscussed in greater detail below, the controller 235 can cause thevalve 230 to introduce a series of one or more pills of the second fluid250 into the flow of the first fluid 126.

Creating a pill of the second fluid 250 in a flow of the first fluid 126within the drill string 108 can be accomplished by, for example,starting from a configuration where the valve 230 is accepting only thefirst fluid 126, switching the valve 230 to accepting only the secondfluid 250 for a certain, predetermined amount of time, then switchingthe valve 230 back to accepting only the first fluid 126. The resultinglength of the pill of the second fluid within the drill string 108 maybe dependent upon several factors including, but not limited to, one ormore of the pressures of the first and second fluids 126,250 at theirrespective inlets 231,232, the size of the respective inlet pipes121,221 for each inlet 231,232, the cross-sectional flow area of thedrill string 108, the length of the drill string 108, the viscosity ofthe first and second fluids 126,250, the type of pumps 120,220 used,combinations thereof, and the like. Taking into account these severalfactors, a desired length of a pill within the drill string 108 can becalculated and correspond to a specific time duration for the valve 230to accept only the second fluid 250 via the second inlet 232. In one ormore embodiments, this information can be stored in the controller 235or calculated as needed by the controller 235.

As shown in FIG. 2, a series of pills 252 of the second fluid 250 hasbeen introduced into the drill string 108. In particular, the series 252depicted in FIG. 2 includes two pills of the second fluid 252 with apill of the first fluid 126 being disposed between the two pills of thesecond fluid 250. In exemplary operation, the series 252 of pills of thesecond fluid 250 may be configured to convey information to the downholetool 140, as discussed in greater detail below with respect to FIGS.5A-5C.

The communication system 200 may also include a sensor 240 located, inthis example, within the drill string 108 near the drill bit 114. Aswill be appreciated, however, the sensor 240 may be located in otherlocations in the downhole environment, such as at any point along thedrill string 108. The sensor 240 may be configured to measure at leastone physical property exhibited by both the first and second fluids126,250. In some embodiments, the second fluid 250 may exhibit a valueof the physical property that is different from that exhibited by thefirst fluid 126, and the sensor 240 may be configured to differentiatebetween the first fluid 126 and the second fluid 250 based on measuringthe corresponding values of the common physical property exhibited byeach fluid 126,250. As will be appreciated by those skilled in the art,any physical property that may be different between the first and secondfluids 126,250, and that is detectable by the downhole sensor 240, maybe used, without departing from the scope of the disclosure. Examplephysical properties include, but are not limited to, temperature of thefluid, viscosity, electrical conductivity, capacitance, thermalconductivity, magnetic field strength, density, opticaltransmissibility, spectral fingerprint, an emitted amount ofelectromagnetic radiation, combinations thereof, or the like.

By measuring the transition time or duration between the differentvalues of a physical property corresponding to the first and secondfluids 126, 250, the sensor 240 may be able to determine a length ofeach pill of the second fluid 250 as it passes or otherwise interactswith the sensor 240. In one or more embodiments, the respectivedurations can be compared to each other without requiring a conversionof the transition time to a measurable length and the relative durationscan then be used in place of lengths of the pills in a defined series ofpills.

In at least one exemplary embodiment, the physical property to bedetected by the sensor 240 may be electrical conductivity of the firstand second fluids 126, 250. Electrical conductivity measurements areoften made during hydrocarbon extraction processes in order tocharacterize rock formations during drilling or otherwise to detectparticular downhole fluids or substances. For instance, conductivitymeasurements are often performed on the drilling fluid (i.e., mud) thatis conveyed into and returned from the borehole 116. In this exemplaryembodiment, the first fluid 126 may be drilling fluid that may exhibit afirst electrical conductivity, and the second fluid 250 may be a fluidchosen or designed to have a different electrical conductivity than thisfirst fluid 126. For instance, the second fluid 250 may be brine or abrine solution exhibits a higher conductivity than the drilling fluid(i.e., the first fluid 126). The detector 240 may be configured todetect the increased conductivity of the second fluid 250, and therebyconclude that a pill of the second fluid is present.

In some embodiments, the physical properties of each fluid 126, 250 maybe entirely different, and the sensor 240 may be configured to detectthe physical property of only the second fluid 250, thereby determiningwhen the one or more pills of the second fluid 250 are present.

It will be apparent to those of skill in the art that the use of thedisclosed communication methods and system are not limited tosubterranean drilling operations and communication with downholeequipment. For example, similar methods and systems may be adapted toany system wherein a first fluid is being transported through a flowpath, such as a tube or pipeline, and a second fluid may be introducedinto the flow in the form of pills in order to digitally communicatewith one or more downstream tools and/or mechanisms. In someembodiments, for instance, an above-ground oil transfer pipeline may usethis method to transfer information or commands from a first point alongthe pipeline to a second point that is downstream from the first point.The pills of the second fluid injected into the flow of the first fluidmay include detectable material, such as a fine magnetic powder, oranother substance that a suitable sensor may be configured to detect andrecognize that a pill of the second fluid is present.

Referring to FIG. 3, with continued reference to FIG. 2, illustrated isa block diagram of an exemplary communicative coupling of the valvecontroller 235 and the downhole tool 140, according to one or moreembodiments. Intermediate elements of the communication path, forexample the valve 230, have been omitted in FIG. 3 to clarify theillustration. Digital messages are sent by the controller 235 in theform of a defined series of pills 252 of a second fluid 250 disposedwithin a flow of a first fluid 126 that is traveling along a flow path(e.g., the drill string 108) to the recipient downhole tool 140. Thedefinition of each message includes the number of pills and the relativelength of each pill in the series, wherein each pill may have the sameor a different length. The controller 235 may include a first library ofmessages, each message comprising a different series of one or morepills. The controller 235 may be configured to accept a selection of oneof the messages from the library and transmit the message by actuatingthe valve 230 (FIG. 3), as generally described above, thereby injectingthe proper series of pills 252 that correspond to the selected messageinto the flow of the first fluid 126.

As discussed above, the downhole tool 140 may include a sensor 240 (FIG.2) and an accompanying processor and memory (not visible in FIG. 3). Thememory may be configured to store a second library of data correspondingto the first library of the controller 235. Upon detecting the pills 252of the second fluid 250, the sensor 240 may be configured to conveyinformation (e.g., length, number, etc.) relating to the sensed pills252 to the processor which compares the conveyed information with thedata stored in the second library, thereby determining which message isbeing received. The message may, in one or more embodiments, include acommand signal intended to be received by the downhole tool 140. Thedownhole tool 140 may be configured to execute the command upon receipt,thereby allowing operators on the surface to initiate specific actionsby the downhole tool 140.

In one or more embodiments, there may be a second communication path 270that places the downhole tool 140 in communication with the controller235 or other surface electronic module (not shown in FIG. 3). The secondcommunication path 270 may be a wired or wireless communication linkallowing the downhole tool 140 to inform the controller 235 of thereceipt of the message or a particular downhole command.

FIGS. 4A-4E depict example messages comprising series 252 of pills ofthe second fluid 250 as injected into a flow of the first fluid 126,according to one or more embodiments. In each of FIG. 4A-4E, the firstfluid 126 is conveyed through a flow path, such as the drill string 108,from left to right. In these examples, each series 252 includes an“attention” portion 254 followed by a “content” portion 256, with aseparation distance 258 between the trailing edge of the last pill ofthe attention portion 254 and the leading edge of the first pill of thecontent portion 256. In one or more embodiments, the separation distance258 comprises at least one of a minimum length and a maximum length. Inone or more embodiments, every message is defined to include a commonattention portion 254. In other embodiments, however, the attentionportion 254 may be omitted from the messaging sequence.

In FIG. 4A, the series 252 includes a content portion 256A that isdefined to be the command “TURN ON,” and would be recognized by thedownhole tool 140 as a trigger to initiate or commence its correspondingfunction. It can seen that this example content portion 256A isconfigured as a first long pill of the second fluid 250 followed by twoshort pills. Between each pill of the second fluid 250 is a spacer pillof the first fluid 126 that serves as a spacer between adjacent pills ofthe second fluid 250. In one or more embodiments, the length of thespacer pills of the first fluid 126 may have at least one of a minimumlength and a maximum length. In embodiments where all messages aredefined to have content portions with three pills of the second fluid250, the content portion 256A and the series 252 are both complete atthe trailing edge of the third pill of the content portion 256A.

FIG. 4B illustrates a similar message with an attention portion 254 anda content portion 256B with a different series of pills than the contentportion 256A of FIG. 4A. This example content portion 256B is configuredto start with two short pills of the second fluid 250 followed by a longpill and this series is defined, for this example, to be a command “SETTO 25%” for a tool 140 such as a valve, wherein 25% may represent anamount that the valve is open, or a rotary tool, wherein 25% mayrepresent the speed of rotation as a percentage of full speed of therotary tool.

FIGS. 4C-4E illustrate additional message portions 256C, 256D, and 256Ethat provide additional example commands of “SET TO 50%,” “SET TO 75%,”and “SET TO 100%,” respectively, wherein the percentages may representdifferent settings for the example tools 140 of a valve and a rotarytool discussed above. While the example commands shown in FIGS. 4A-4Eare each defined with a three-pill content portion 256, where the pillswithin each content portion are either a “short” length or a “long”length, it will be apparent to those of skill in the art that the numberof pills and their respective lengths may vary, without departing fromthe scope of the disclosure. Accordingly, numerous digital commands maybe sent by varying the numbers and lengths of the respective pills,thereby communicating with the downhole tool 104 to undertake equallynumerous tasks.

Referring now to FIGS. 5A-5C, with continued reference to FIG. 2,depicted is an example message as it is conveyed from the valve 230 tothe downhole sensor 140, according to one or more embodiments. The firstand second fluids 126, 250 may have different measured values of atleast one physical property. As described above, the valve 230facilitates fluid flow of each of the first and second fluids 126, 250down through the drill string 108 and past a downhole tool 140 arrangedtherein. The sensor 240, positioned at a second point along the drillstring 108, may be configured to detect the difference in the at leastone physical property between the first and second fluids 126, 250,thereby determining which fluid is passing the second point at any giveninstant in time. In this example, the valve 230 allows flow exclusivelyfrom either the first or the second fluids 126, 250 and does not includea configuration that shuts off the flow from both fluids 126, 250 at thesame time. The diameter of the drill string 108 and the relative lengthsof the pills are not shown to scale in FIGS. 5A-5C and intended only toillustrate the concepts. In one or more embodiments, the lengths of thepills of series 252 may be larger than the diameter of the drill string108. In one or more embodiments, for example, the lengths of the pillsin series 252 may be several times the diameter of the drill string 108or longer.

FIG. 5A illustrates the state of the fluids 126, 250 within the drillstring 108 at a first time T1 just after the valve 230 has completedinjecting the last pill of the second fluid 250 for a series 252 ofpills that corresponds to a particular message (e.g., the messageillustrated in FIG. 4A). The series 252 includes an attention portion254 with three short pills of the second fluid 250 followed by a contentportion 256 that includes a first long pill followed by two short pills.

FIG. 5B illustrates the configuration of this same drill string 108 at asecond time T2, at which time the trailing edge of the last pill 255C ofthe attention portion 254 is passing the sensor 240 located at thesecond point along the flow path of the drill string 108 and the sensor240 has passed information to the downhole tool 140 that three shortpills have been detected. At this point, the tool 240 is aware that acommand is about to arrive and may, in certain embodiments, run certainsets of instructions or otherwise reconfigure itself in preparation forreceiving the command.

FIG. 5C illustrates the configuration of this same drill string 108 at athird time T3, at which time the trailing edge of the last pill 257C ofthe content portion 256 of the series 252 is passing the sensor 240located at the second point along the flow path of the drill string 108and the sensor 240 has passed information to the downhole tool 140 thatone long and two short pills have been detected. The downhole tool 140compares this series 252 of pills to the message definitions storedinternally within the downhole tool 140 and determines which messagecorresponds to the detected series of pills of the second fluid, therebyreceiving the message that was sent using the valve 230.

FIGS. 6A and 6B illustrate the an exemplary configuration of a series254 of pills of a second fluid 250 injected into a flow of a first fluid126 through a pipe 600, according to one or more embodiments. It can beseen in FIG. 6A that the pills of the second fluid 250 have sharplydefined end surfaces 260 or boundaries. Plotting the value of aparticular physical property, for example electrical conductivity, alongthe length of the pipe 600, wherein the first fluid 126 has a “LO” valueand the second fluid 250 has a “HI” value, produces a waveform or curve610, as shown in FIG. 6B. It can be seen that the curve 610 sharplytransitions between the HI and LO values and may be considered to be asquare wave. Each portion of the curve 610 between a LO-to-HI transitionand a subsequent HI-to-LO transition, an example of which is indicatedby the dashed-line oval labeled 612 in FIG. 6B, may be considered to bea “pulse” of the second fluid 250 in the flow of the first fluid 126.Thus, the pills of the second fluid 250 in the series 252 may beconsidered to be equivalent to pulses 612 in a conventional signal. Eachpulse 612 has an associated length 614 that is clearly defined in thecurve 610.

FIGS. 7A and 7B illustrate a downstream configuration of the same series252 of pills of a second fluid 250 injected into a flow of a first fluid126 through a pipe 600, according to one or more embodiments. As theseries 252 flows through the pipe 600, turbulence within the fluids 126and 250, as well as viscous friction with the walls and flowdisturbances created by intermediate piping elements such as couplingand valves (not shown in FIG. 7A) may tend to cause mixing of the fluids126 and 250 at the boundaries 260. After some period of time, theboundary 260 of FIG. 6A may no longer be distinguishable but, instead, atransition zone 262 may be generated. A measured value of the particularphysical property may gradually and continuously vary across thistransition zone 262 and, when the value is plotted as before along thelength of the pipe 600, produces the curve 620 shown in FIG. 7B. It canbe seen that the value of the curve 620 varies gradually and it may notbe a simple matter to define a transition point between a HI state and aLO state and, subsequently, difficult to determine a length of a pulse614.

The integrity, or coherence, of the pills of the second fluid 250 andthe first fluid 126 decreases as the length of the transition zone 22increases. In certain embodiments, the series 252 may be considered tobe coherent if it is still possible to detect the individual pills ofthe second fluid 250 and thereby receive the message of the series 252.As the distance traveled by the series 252 in the pipe 600 increases,the length of the transition zone 262 may increase until there is nolonger a portion of the original pill of the second fluid 250 that ispure second fluid 250, whereupon the determination of a HI state bydetecting the value of the physical parameter of the pure second fluid250 is no longer possible. In certain embodiments, however, it ispossible to extend the distance over which a series 252 retainscoherence by use of alternate criteria for detecting a pill of thesecond fluid 250.

In certain embodiments, the boundaries of a pulse 614 may be defined bythe directional crossing of a threshold value that is different than thevalues associated with the pure fluids 126 and 250. In certainembodiments, a HI threshold may be established that, in this example, isless than the HI value of curve 610 and, similarly, a LO threshold maybe established that is greater than the LO value of curve 610. Incertain embodiments, a length 615 may be determined as the distancebetween a LO-to-HI transition of curve 620 across the HI threshold and asubsequent HI-to-LO transition across the same HI threshold. In certainembodiments, a length 616 may be determined as the distance between aLO-to-HI transition of curve 620 across the LO threshold and asubsequent HI-to-LO transition across the same LO threshold. In certainembodiments, a length 617 may be determined as the distance between aLO-to-HI transition of curve 620 across the HI threshold and asubsequent HI-to-LO transition across the LO threshold. In certainembodiments, other thresholds may be established and different criteriaapplied for determining a boundary between a pill of the second fluid250 and the first fluid 126.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

The invention claimed is:
 1. A method of communicating, comprising:providing a flow of a first fluid along a flow path; introducing aseries of one or more pills of a second fluid into the flow of the firstfluid at a first point along the flow path; and detecting the series ofone or more pills of the second fluid at a second point along the flowpath, the second point being separated from the first point.
 2. Themethod of claim 1, wherein the first fluid comprises a drilling fluid.3. The method of claim 1, wherein: the first fluid exhibits a firstvalue of a physical property; and the second fluid exhibits a secondvalue of the physical property that is different from the first value.4. The method of claim 3, wherein the physical property is electricalconductivity.
 5. The method of claim 4, wherein the second fluidcomprises a brine.
 6. The method of claim 3, wherein the physicalproperty is density.
 7. The method of claim 3, wherein the physicalproperty is magnetic field density.
 8. The method of claim 3, whereinthe physical property is spectral fingerprint.
 9. The method of claim 1,further comprising separating axially adjacent pills of the second fluidwith a pill of the first fluid.
 10. The method of claim 1, wherein: eachpill of the series of one or more pills comprises a respective length; afirst pill of the series of one or more pills comprises a first length;and a second pill of the series of one or more pills comprises a secondlength not equal to the first length.
 11. The method of claim 10,further comprising: defining a message with the series of one or morepills of the second fluid, wherein the series comprises a predeterminednumber of pills, each having a predetermined respective length; sendingthe message by introducing the series of one or more pills of the secondfluid into the flow of the first fluid at the first point; detecting theseries of one or more pills of the second fluid with a sensor that isarranged within the flow path at the second point; and receiving themessage by determining the message associated with the detected seriesof pills.
 12. The method of claim 11, wherein the sensor is communicablycoupled to a downhole tool, the method further comprising: executing afunction of the downhole tool that is associated with the receivedmessage.
 13. The method of claim 11, wherein each message comprises anattention portion and a content portion.
 14. A communication systemcomprising: a fluid valve having a first input fluidly coupled to asource of a first fluid exhibiting a first value of a physical property,a second input fluidly coupled to a source of a second fluid exhibitinga second value of the physical property, and an output fluidly couplingthe first and second inputs to a flow path; a controller communicativelycoupled to the fluid valve and configured to actuate the fluid valve soas to provide a flow of the first fluid to the flow path and introduce aseries of one or more pills of the second fluid into the flow of thefirst fluid; and a sensor arranged within the flow path and configuredto detect the physical property and differentiate between the firstvalue and the second value, thereby detecting the series of one or morepills of the second fluid.
 15. The communication system of claim 14,wherein: the controller comprises a library of messages, where eachmessage comprises a distinct series of one or more pills of the secondfluid by exhibiting a predetermined number and corresponding length ofeach of the one or more pills of the second fluid; the controller beingconfigured to accept a selection of a message from the library andactuate the fluid valve to create the series of one or more pills of thesecond fluid that correspond to the message selected, thereby conveyingthe message within the flow path; and the sensor being furtherconfigured to provide information on the predetermined number andcorresponding length of each of the one or more pills in each distinctseries.
 16. The communication system of claim 14, wherein the firstfluid comprises a drilling fluid and the second fluid comprises a spacerfluid.
 17. The communication system of claim 15, wherein the library ofmessages is a first library, and the sensor comprises a second libraryof messages and is configured to determine which message corresponds tothe detected series of one or more pills of the second fluid, therebyreceiving the selected message.
 18. A method of communicating with adownhole tool, the method comprising: providing a flow of a drillingfluid from a surface valve through a drill string to the downhole tool,the drilling fluid exhibiting a first value of a physical property;introducing one or more pills of a spacer fluid into the flow of thedrilling fluid via the surface valve, the spacer fluid exhibiting asecond value of the physical property that is different from the firstvalue; and detecting the one of more pills of the spacer fluid at thedownhole tool.
 19. The method of claim 18, wherein the physical propertycomprises a physical property selected from the group consisting ofelectrical conductivity, density, magnetic field strength, and spectralfingerprint.